In order to satisfy the increasing requirements for the data services of people's, the 3rd Generation Partnership Project (3GPP) starts the Long Term Evolution (LTE) project of the 3G system, which aims at providing stronger data service support and providing better services for users by the successively evolved 3G systems. The LTE system adopts the Orthogonal Frequency Division Multiplexing (OFDM) transmission technique, which improves the spectrum efficiency and the robustness of the system to the frequency selective channel.
In the radio communication system, when the UE is just powered on, is idle and is in the activated state, the UE is required to perform the cell search to obtain more detailed information about the cell and adjacent cells, so as to initiate other physical layer processes. The performance of the cell search directly affects the performance of the whole system. In the cell search process of the LTE system, UE not only should be synchronized with the serving cell in the time and frequency, but also should detect the physical layer cell identifier of the cell. The available system characteristic for implementing the cell search is the synchronization signal. The synchronization signal in LTE includes the Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS). Generally, the primary synchronization signal is mainly used for obtaining the 5 ms timing, and sector-ID identification and the like; the secondary synchronization signal is mainly used for implementing the radio frame timing synchronization and cell ID identification and the like.
The time domain structure of the synchronization signal is as shown in FIG. 1. PSS and SSS use the time division multiplexing, and are sent twice in one 10 ms radio frame, namely, once every 5 ms. As for the specific cell, the PSS signals sent twice in one frame are the same, which can act as the 5 ms timing; the SSSs sent twice in one frame are different, which can be used for implementing the 10 ms timing. As for the type of the Frequency Division Duplexing (FDD) frame structure (as shown in FIG. 1A), PSSs are situated at the last symbols of the 0th and 10th slots, and SSSs are situated at the previous symbols of PSSs. As for the type of the Time Division Duplexing (TDD) mode frame structure (as shown in FIG. 1B), PSSs are situated at the 3rd symbols of the sub-frame 1 and sub-frame 6; SSSs are situated at the last symbols of the sub-frame 0 and sub-frame 5, that is, SSS is at the 3rd symbol before PSS. In the frequency domain, the synchronization signal is always transmitted at the central position of the downlink transmission bandwidth of the destination cell, and always occupies the intermediate 1.08M bandwidth (PSS and SSS respectively occupy the intermediate 62 sub-carriers of the OFDM symbol, and other 10 sub-carriers are reserved sub-carriers) no matter how the system bandwidth is configured. Although UE does not known the system bandwidth in advance, the fast, low complexity and low overhead cell search can be ensured in different bandwidth configuration.
The secondary synchronization signal detection acts as a very important stage of the cell search, and the prior art proposes two types of detection methods. The Chinese patent application published on 7 Oct. 2009, of which the application number is CN200910078544.9 and the published number is CN101552762A, proposes a method and an apparatus for detecting a cyclic prefix length type and a secondary synchronization signal. It calculates the secondary synchronization signal positions in different cyclic prefix length types according to the primary synchronization channel positions detected through the primary synchronization signals to obtain the secondary synchronization signals, performs the pairwise correlation calculation on the secondary synchronization signals and the replica of secondary synchronization signals in the frequency domain to obtain multiple correlation powers, and detects the maximum value in the multiple correlation powers, thereby determining the practically adopted cyclic prefix length type as well as the cell ID and the radio frame timing. This method uses a method for noncoherent detection, and comparing with the coherent detection, its detection performance has greater degradation, and its correlation calculation uses the total sequence detection, which has the very high computational complexity.
The US patent application US20080273522A1 published on 6 Nov. 2008 proposes a method for generating and detecting a secondary synchronization signal. It performs channel estimation on corresponding received secondary synchronization signals through the received primary synchronization signal, thereby completing the coherent detection of the secondary synchronization signal and further obtaining the cell ID and the radio frame boundary. As for the correlation calculation in the detection, this patent application uses the Fast M-sequence Transform (FMT), which is transformed into the Fast Hadamard Transform (FHT) by the SSS sequence transforming and address mapping. With this method, the computational complexity of the correlation calculation is more greatly reduced, however, the implementation process introduces more address mapping and de-mapping, which additionally increases the resource consumption.